The present invention relates to a coloring composition for color filter containing a colorant and a color filter using the coloring composition, and more particularly, to a coloring composition for color filter containing a colorant exhibiting not only a sharp particle size distribution but also excellent light resistance, and a color filter using such a coloring composition, which exhibits excellent spectral properties.
In the recent computerized society, various information devices such as personal computers or the like have rapidly spread in any of business, personal and domestic applications. These information devices are almost provided with a display as one of terminal equipments thereof. In particular, since portable-type information devices are required to have a lightweight and a small size for space-saving, a liquid crystal display (LCD) devices, especially color LCD devices, have been used therein.
A color filter is essential to express the information by the color LCD devices. The color filter is an optical filter constituted by three primary colors of either R (red), G (green) and B (blue) or C (cyan), Y (yellow) and M (magenta) regularly arranged on a glass plate.
The color LCD devices have been first required to show a good color property (color-reproducing property), a high lightness and a large contrast. With these requirements, the color filter used in the color LCD devices have also been required to have a higher performance as to color property (color-reproducing property), a lightness and a contrast thereof.
The color property of the color filter can be improved by increasing a concentration of pigments contained therein so as to enhance its color density. However, the increased pigment concentration causes the deterioration in light transmittance of the color filter. Therefore, in general, the color property of the color filter has been improved by enhansing a color purity of a colorant used in the color filter, i.e., by using a colorant having a narrower transmission spectrum.
In order to obtain a colorant having a high color purity, there has been generally used the method of mixing the respective three primary colors R (red), G (green) and B (blue) with corresponding complementary colors, i.e., a so-called subtractive color mixing method (Japanese Patent Application Laid-Open (KOKAI) Nos. 8-295808(1996), 8-295809(1996) and 2001-188120, etc.).
In order to enhance a lightness of the color filter, pigments used in the color filter are required to have a high transparency and an excellent dispersibility.
Hitherto, dyes have been used as a colorant for the color filter from the standpoints of transparency, fluidity, dispersibility and the like. However, these dyes are chemically active and, therefore, deteriorated in fastness such as light resistance. For this reason, in recent years, pigments are mainly used as the colorant of the color filter.
However, since the pigments are in the form of particles unlike dyes dissolvable in vehicle, when such pigments are used, it has been difficult to obtain color filters having a high transparency corresponding to that of color filters using the dyes. In order to improve the transparency, there has been proposed the method of filling up colloid particles having a particle size of less than 100 nm between colorants having a particle size of more than 200 nm (Japanese Patent Application Laid-Open (KOKAI) No. 2001-126635).
Also, in the case of organic pigments, from pigments kept in a molecular state to pigments composed of fine primary particles having a particle size of about 20 to 100 nm are produced by the chemical reaction or the like. However, the fine primary particles or the like have a very high surface energy and, therefore, tend to be agglomerated together. As a result, the fine primary particles or the like are usually formed into aggregates, i.e., secondary particles having a very large particle size. For this reason, it has been required to develop techniques for obtaining finely divided pigments.
As the method of obtaining finely divided pigments, there are known a method of controlling crystal growth of pigments during the production process thereof; a method of mechanically pulverizing the pigments; or the like. However, in any of these methods, the obtained pigments tend to have a broader particle size distribution and an uninformed particle shape, resulting in tendencies of deteriorated contrast due to light scattering as well as poor dispersibility in vehicle.
For these reasons, there has been required a colorant for color filter, which has a fine particle size and a sharp particle size distribution.
Conventionally, in order to obtain color filters having excellent light transmittance and contrast, there have been proposed the methods using pigments having a specific particle size (Japanese Patent Publication (KOKOKU) Nos. 4-37987(1992) and 4-39041(1992), Japanese Patent Application Laid-Open (KOKAI) No. 9-197118(1997), etc.).
In addition, the color filters have been required to show a high reliability upon outdoor use, such as a high light resistance.
At present, it has been strongly required to provide a color filter having excellent spectral properties, using a colorant for color filter capable of exhibiting not only a sharp particle size distribution but also excellent transparency. However, the conventional colorants have failed to satisfy these requirements.
That is, in Japanese Patent Application Laid-Open (KOKAI) Nos. 8-295808(1996), 8-295809(1996) and 2001-188120, there is described the method of improving spectral properties of the color filter by a subtractive color mixing method using pigments having a specific particle size therein. However, since the pigments used have a broad particle size distribution, the spectral properties of the color filter cannot be sufficiently improved.
Also, in Japanese Patent Application Laid-Open (KOKAI) No. 2001-126635, there is described the method of improving the transparency by filling up colloid particles having a particle size of less than 100 nm between colorants having a particle size of more than 200 nm. However, the adhesion strength between the colloid particles and the colorant is insufficient, thereby causing deterioration of dispersibility in vehicle and failing to obtain the effect of sufficiently improving the transparency.
In Japanese Patent Publication (KOKOKU) Nos. 4-37987(1992) and 4-39041(1992) and Japanese Patent Application Laid-Open (KOKAI) No. 9-197118(1997), there is described the method of using pigment particles having a specific particle size. However, since the reduction of the particle size of the pigment particles is conducted by mechanical pulverization, the obtained particles failed to show a uniform particle shape and a sufficiently sharp particle size distribution.
Meanwhile, in Japanese Patent Application Laid-Open (KOKAI) No. 2001-226609, there are described green-based pigments composed of green composite iron oxide hydroxide particles comprising iron oxide hydroxide particles; a coating layer formed on the surface of the iron oxide hydroxide particle, which comprises organosilane compounds obtainable from alkoxysilanes, or polysiloxanes; an organic blue pigment coat formed on the coating layer. However, the technique described in this KOKAI is to fixedly adhere the organic blue pigments onto the yellow iron oxide hydroxide particles and, therefore, is quite different from the technique of the present invention for obtaining the organic pigments having a high chroma. Further, in this KOKAI, there is neither taught nor suggested the motivation for applying the green-based pigments to a colorant for color filter.
As a result of the present inventors' earnest studies for solving the above problems, it has been found that by using a colorant composed of composite particles having an average particle diameter of 0.001 to 1.0 μm, which comprise white inorganic particles, a gluing agent coating layer formed on the surface of the white inorganic particle and an organic pigment coat formed onto the gluing agent coating layer, and exhibits not only a sharp particle size distribution but also excellent light resistance, the obtained color filter exhibits excellent spectral properties. The present invention has been attained on the basis of the findings.